The collection and reinfusion of a patient's own blood, referred to as autologous blood, offers a number of recognized benefits. For example, the use of autologous blood reduces concerns relating to the possibility of disease transmission via donor blood transfusions, referred to as homologous blood, as well as concerns regarding febrile/allergic reactions. Additionally, autologous blood recovery ensures the rapid availability of blood and reduces or eliminates the need for compatibility testing on such blood since the procedure is most typically completed in an operating room. Further, the use of autologous blood provides red blood cells which are generally superior in quality to banked blood and reduces any quantity of homologous blood otherwise needed. The use of autologous blood is also desirous to many patients for psychological and/or religious reasons.
Intraoperative procedures where autologous blood salvage is currently employed include cardiac and vascular surgery. Specialties which employ autologous blood salvage include orthopedics, plastic and reconstructive surgery, neurosurgery, solid organ transplants, general surgery, gynecology and trauma.
In a typical blood salvage procedure, blood is removed from or about a surgical site via a hand-held suction device, mixed with an anticoagulant, and transferred to a reservoir for subsequent transfer for batch processing. In connection with such collection/transfer of salvaged blood, the blood is typically filtered to remove debris and defoamed to remove entrained gaseous components (e.g. air) utilizing separate in-line filter devices and defoaming devices through which the salvaged blood is sequentially transferred. During batch processing, the salvaged blood and a wash solution are separately pumped in sequence through a centrifuge to separate red blood cells and achieve a degree of washing. Following processing, the red blood cells are removed from the centrifuge for reinfusion to the patient.
As can be appreciated, in completing a blood salvage operation, it is desirable to utilize an amount of anticoagulant that is sufficient to adequately address clotting to avoid line blockage and to further allow for maximum recovery of red blood cells. On the other hand, too much anticoagulant may result in not only waste and added fluid storage components, but additionally may result in unused anticoagulant being contained with the collected red blood cells, thereby compromising hemostasis upon reinfusion. Of further note, even when an appropriate amount of anticoagulant is utilized, the anticoagulant needs to achieve adequate mixing with the salvaged blood in order to achieve the desired relative concentration. To address this consideration, heparin is often employed since it diffuses quickly and is quite effective in preventing clots in low concentrations. Heparin may cause a number of adverse side effects, however, including, for example, post-operative bleeding from unneutralized heparin rebound, platelet activation, and allergenic reaction. Consequently, an acid citrate dextrose (ACD) anticoagulant may be preferred in many instances. ACD exhibits mixing difficulties, however, and is quite sensitive in relation to achieving the desired anticoagulant/blood ratio.
As to filtration, the desired capability to remove small debris must be balanced in relation to any potential filter plugging implications. That is, as filter pore sizing is decreased, the potential for filter plugging is increased. Such filter plugging presents particular design challenges where, for example, available filtration surface area is limited. Consequently, many blood salvage processes currently employ filters having 120 .mu. openings as opposed to a finer 40 .mu. opening since significant plugging would occur if 40 .mu. filters were employed.
With regard to the filtration, defoaming and blood processing steps in typical blood salvage procedures, the primary objectives are to obtain a high quality and amount of collected red blood cells in the least amount of overall procedure time. In this regard, the above-described separate filtration, and defoaming and steps, the separate red blood cell separation and wash steps on a batch basis, present significant tradeoff limitations between achieving a high-quality blood product and reducing overall procedure time requirements.